The present invention relates, in general, to the field of fossil-fueled (particularly coal fired) steam generators used in the production of steam for industrial processes or electric utility power generation. In particular, the present invention is drawn to a baffle for increasing the capture of ash in hoppers so that downstream equipment, such as selective catalytic reduction (SCR) devices, are not subjected to excessive amounts of ash which might otherwise plug the catalyst used in such SCR devices and render them ineffective.
Persons skilled in the art of industrial and utility boiler design used in the production of steam for industrial processes or electric utility power generation are quite familiar with such devices and thus the particular details regarding same have been omitted herein for the sake of conciseness and readability. For further details of such industrial and utility boiler installations, as well as a description of various types of environmental clean-up equipment such as SCR's used in combination with such steam generator equipment, the reader is referred to STEAM/its generation and use, 40th Edition, Stultz and Kitto, Jr., Eds., Copyright© 1992 The Babcock & Wilcox Company, the text of which is hereby incorporated by reference as though fully set forth herein.
A set of hoppers can normally be found below the economizer gas outlet of such steam generators. The flue gas and entrained ash particles produced as a byproduct of the combustion of a fossil fuel such as coal is conveyed through the steam generator in order to transfer heat to water and steam used in the industrial process or sent to a steam turbine in order to produce electricity, in a manner well known to those skilled in the art. As the entrained fly ash settles out of the flue gas flow, it falls into these hoppers and then is removed either pneumatically or mechanically.
There have been a number of recent events in the industry in which the top catalyst layers of an SCR system provided to reduce NOx emissions from such steam generators have become plugged with popcorn ash. This blockage can cause increased pressure drop, decreased catalyst performance, and under the worst circumstances can force an SCR system to be taken off line. Popcorn ash is a type of large particle ash which is light, porous, irregularly shaped, and often forms in the upper furnace or on the convective section heat exchanger surfaces of such steam generators. Popcorn ash particles can easily reach a size of up to ten millimeters or more. With standard flue gas outlet and hopper designs a portion of these large particles usually does not get captured. Particles greater than four or five millimeters in size have been known to cause SCR catalyst plugging.
Some past solutions to this problem have involved placing flat baffles between the economizer and the hoppers and/or by placing wire mesh screens across the outlet flue. The flat baffles create a tortuous path for the flue gas flow which the large particles cannot follow. The wire mesh screen physically blocks the large particles while allowing the flue gas to flow through.